Differential transformer control device



Patented Ma; 16, 1950 UNITED DIFFERENTIAL TRANSFORMER CONTROL DEVICE Gerard H. Caine, Hamilton, Ohio, assignmto Minneapolis-Honeywell Regulator Company,

Minneapolis, Minn., a corporation of Delaware Application March 5, 1945, Serial No. 581,043

9 Claims. 1

My invention relates to electric control devices and has for an object to produce a control device responsive to a feeble actuating force and operating to produce an appreciable corresponding controlling force.

Another object of the invention resides in providing a control device utilizing two core members, one having an elongated portion provided with a distributed winding and the other having a pole disposed adjacent said distributed winding and having an'exciting winding thereon, and in further providing means for supporting said distributed winding and poles for relative movement.

Another object of the invention resides in constructing the distribtued winding in arcuate form and in pivoting said core member having the pole and said distributed winding for relative movement about the axis of the said distributed winding.

A still further object of the invention resides in providing an electric control device in which the electromotive force induced in the distributed winding is substantially proportional to the extent of the relative movement of the pole and the distributed winding.

Another object or the invention resides in providing an electric control device adapted to be energized by alternating or pulsating current and in which a constant phase shift may be made to exist between the electromotive force of the input and output windings throughout a range of relative motion thereof.

Another object of the invention resides in providing an electric control device including a magnetic structure providing two magnetic circuits, one including the portion of the elongated core member to one side of the core member having the pole and the other including the portion of said elongated core member to the other side of the core member having the pole, said core member having the pole being common to both circuits.

A still further object of the invention resides in providing an electric control device in which the reluctance of the two magnetic circuits remains substantially the same throughout the movement 01' the movable core member.

A feature of-the invention resides in providing a control device in which such a small power transfer occurs between the input and output windings, that there are no appreciable changes in the reluctances of the magnetic circuits and so that no appreciable resistance to the movement of the movable core member results.

an'electrlc control device in which the movement of the movable core member may exceed 180.

Another object of the invention resides in providing an electric control device in which no sliding or moving contacts need be employed.

A still further object of the invention resides in providing an electric control device in which the phase of the electromotive force induced in the distributed winding produces a phase reversal of 180 upon movement of the movable member from one side of the null point to the other.

Other objects of the invention reside in the novel combination and arrangement of parts and in the details of construction hereinafter illustrated and/ or described.

In the drawings:

Fig. 1 is a wiring diagram of an electric control device illustrating an embodiment of my invention.

Fig. 2 is a wiring diagram or a modification of the structure shown in Fig. 1.

Fig. 3 is a wiring diagram of still another form of the invention.

Fig. 4 is a wiring diagram of another form of the invention.

Fig. 5 is an elevational sectional view taken on line 5-5 of Pig. 4.

Fig. 6 is a diagrammatic view of still another form of the invention.

Fig. 7 is a diagrammatic view of a still further modification of the invention.

In control devices formerly employed utilizing relatively movable core members, one of the difliculties encountered has been that the reluctances of the magnetic path or paths would vary upon relative movement of the core members, thus affecting the accuracy and operation of the device and also producing added resistance to the movement of the movable core member. The instant invention overcomes this disadvantage by providing a. construction in which the reluctance of the two magnetic paths are at all times substantially equal and in which a minimum resistance to the operation of the device is produced.

My control device may be used in any of the different ways in which such devices are usually employed. Such devices may be connected to any indicating apparatus, as for example, a meter or any form of signalling apparatus or the same may be connected to a device which is adapted to occupy either of two positions, as, for example, a switch or shut-oflf valve. In such An object of the invention resides in providing case. only a single control device is employed.

If desired, however, the invention may be used in a follow-up system in which case two devices are employed, one connected to and responsive to a variable condition of the actuating device and the other functioning to control the operation of the device intended to be operated in accordance with the variation of the condition to which the actuating device responds. It will be readily apparent that any of the modifications shown in the drawings may be used in any of the systems above referred to.

In Fig. 1, I have shown two control devices I and III! which are connected for use in a follow-up system such as would be suitable for operating a rheostat of an electrically energized furnace to be maintained at a constant temperature. Since these devices are identical in construction, only the control device III will be described in detail and the same reference numerals, preceded by the digit 1 will be used to designate the corresponding parts of the control device H0.

The control device I0 shown in Fig. 1 comprises a core structure indicated in its entirety by the reference numeral II, which includes two core members I2 and I3. The core member I2 is toroidal or continuous in form and for the sake of convenience in the description of the invention, has been considered as consisting of a left hand section I4 and a right hand section which meet at the upper and lower portions of said core section. The two sections I4 and I5 are arcuate and they have a common center which is the center of the member l2.

The core member I3 is an elongated or discontinuous member extending diametrically across the toroidal core member I2 and has two poles I6 and II which are disposed in close proximity to the inner surfaces I8 and I9 of the sections I4 and I5 of core member I2. The core member I3 is pivoted on a shaft 2| concentric with the center 20 of the core member I2. The poles I6 and IT, as the core member I3 rotates, travel along the arcuate surfaces I3 and I9 of sections I4 and I5. By means of the magnetic core structure I I, two magnetic circuits are provided which are digrammatically indicated by dotted lines 22 and 23. The circuit 22 includes the portions of the sections l4 and I5 above the core member I3 and the circuit 23 includes the portions of the sections I4 and I5 of the core member I2 below the core member I3. Core member I3 is common to both of these circuits and, likewise, the air gaps 24 and 25 formed between the ends of the poles I6 and ll of the core member l3 and the surfaces I8 and I3 of the sections I4 and I5.

Wound on the core member I3 is an exciting or input winding 26 which is adapted to be energized by means of any suitable source of alternating or varying current. For this purpose, I have shown in the diagram a transformer 21 having a primary 28 adapted to be connected to an alternating current line 3|--32. This transformer has a secondary 29 which is connected by means of conductors 33 with one side of the winding 26. The other side of the secondary 29 is connected by means of conductors 34 with a variable choke 35. Choke 35 is connected by means of a conductor 36 with a variable resistance 31, which, in turn, is connected by means of a conductor 38 with the other side of the winding 26. It will thus become readily apparent that when the transformer 21 is energized, alternating fluxes are produced in the magnetic cir- 4 cuits 22 and 23 which are opposed to one another in the portions of the core sections I4 and I5 on opposite sides of the locality of the poles I6 and H of the core member I3.

The winding I26 of the control device III! is connected similarly to the winding 26 of the control device III and to the transformer 21 and energized thereby. For this purpose, a conductor I33 is employed which is connected to the conductor 33 and to one end of the winding I26. Another conductor I34 is connected to the conductor 34 and to a choke |35. This choke is connected by means of a conductor I36 with a resistance I31 which, in turn, is connected by means of a conductor I38 with the other end of the winding I26. In the connection of the windings 26 and I26 to the source, the direction of the flow of current is such that the instant polarity of the corresponding poles of the core members I3 and H3 is the same.

Mounted on the core section I5 is a distributed winding 4| which serves as the output winding and which extends substantially throughout the entire extent thereof, namely, throughout an angle of This winding is closely wound on said core section and the pole ll of the core member I3 moves in close proximity to the conductors of said winding disposed on the surface I9 of said core section. In other words, the conductors of the winding 4| disposed along the surface I9 of core section I5 successively pass through the air gap .25 as the core member I3 rotates. For the purpose of explaining the invention, the portion of the winding 4| above the core member I3 has been designated by the reference character 4|, while the portion of the winding 4| situated below the pole I! has been designated by the reference character 4|. From an inspection of Fig. 1, it will readily become apparent that the flux in circuit 22 threads through the portion 4| of winding 4| in one direction and the flux in circuits 23 threads through the portion 4| of winding 4| in the opposite direction. When the core member I3 is disposed at the proper intermediate position, the two fluxes threading through the winding 4| produce electromotive forces in the portions 4| and 4| of said winding which exactly balance one another, so that no current flows through the said winding. This position of the core member I3 has been referred to as the null point of the said core member. When, however, the core member I3 is moved by an extraneous force to one side or the other of its null point, the electromotive force set up in the portions 4| and 4| of the winding 4| become different, due to the fact that a greater or lesser number of turns of the said winding are affected by the fluxes in the respective magnetic circuits 22 and 23. This causes the electromotive force generated in one of said portions to predominate and to cause a flow of current through the winding. The phase of the resultant electromotive force across the winding 4 I, due to the directions of the fluxes in the magnetic circuits 22 and 23, reverses as the core member I3 passes from a position on one side of the null point and to a position on the other side of the null point.

One end of the output winding I of control device I III is grounded. The other end of this winding is connected by means of a conductor I5| with the corresponding end of the winding 4| of control device ID. The other end of the winding 4| is connected by means of a conductor I52 with an amplifier I53. Inasmuch as ampli- 8 ilers are well known in the art, the same has been indicated diagrammatically. The amplifier I53 is connected by means of a conductor I54 with ground. The amplifier I53 controls the operation of an alternating current motor I55 which is of such type that the said motor reverses in rotation upon reversal of phase of the electromotive force energizing the same. The motor I55 has a shaft I53 which is geared or connected by means of any other suitable transmission with the shaft 2| of core member I3 of control device ll (not shown). The said motor, when set in operation, will cause the core member II to shift in one direction or the other, depending upon the direction of rotation of said motor. The motor I55 is energized from the transformer 21 by means of two conductors I51 and I56 which are connected to the conductors 33 and 34, respectively.

The movable core member II3 of control member III! is connected to the actuating device with which the invention is to be used in any suitable manner, such as a thermostat. Where the actuating or a condition responsive device has a rotating shaft, the core member H3 may be mounted directly on this shaft or driven from said shaft. When the shaft of the condition responsive device moves the core member II3 to one side or the other of the null point, the number of turns aifected by the fluxes in the two magnetic circuits becomes different and the electromotive force set up in the portions HI and HI" of winding I will become unbalanced, one of them prevailing and causing an electromo- Iiive force having a certain phase and value across the said winding I. This electromotive force will operate to cause the flow of current through the windings HI and H and also the amplifier I53. The amplifier I53, in turn, will amplify the E. M. F. impressed upon it and control the operation of the motor I55, causing the said motor to turn in one direction or the other, depending upon the phase of the E. M. F. impressed upon it. The motor I55 is so connected up that it rotates the core member I3 in a direction to cause the flux set up by the winding 26 to counterbalance the flux produced by the current from the winding I. When the two fluxes become neutralized, no current flows through the winding H and the motor I55 stops. The rotor I3 is connected to the apparatus to be controlled, which, in the case of a temperature-controlled furnace, would be the rheostat employed for controlling the heating element of the furnace. In such case, the rotor I3 would hold the rheostat at just the proper setting to give the desired amount of heat. The rheostat would then continue to operate at such setting until the thermostat operating the rotor II3 would shift the said rotor and again cause the amplifier and motor I55 to correspondingly adjust the rheostat.

By means of the chokes 35 and I35 and the resistances 31 and I31, the phase angle between the input and output electromotive forces of the two control devices might be modified so that the electromotive forces set up in the two control devices would be completely cancelled out when the rotors of these devices were at their null 'points. Such construction would also be particularly advantageous where several control devices actuated by different actuating devices were used to control a single responding control device.

In Fig. 2 of the drawings, I have shown a modification of the invention in which certain of the parts are simiiiar to those shown in Fig. 1. For the sake of convenience, I will refer to the corresponding parts by the same reference numerals. to which have been added the suffix a, and the description of these parts will not be repeaterd. In the form of the invention shown in Fig. 2, the core member I2a is similarly a continuous member and is mounted for rotation about the center 23a thereof. For this purpose, two arms 46 and 41 are employed which are attached to a hub 48 mounted for rotation on shaft 2 la which arms are also attached to the sections Ia and H211 of the said core member I2a. In this case, the core member "a is a discontinuous member and is provided with poles I6a and Na, which lie in proximity to the outer surface 49 of the core member lia instead of the inner surface, as with the other form of the invention. The poles I66: and Ho are connected by means of a connecting portion 5I which encircles the core member In. In this form of the invention, the core member having the exciting winding thereon is stationary, while the toroidal core member having the distributed winding therein is rotatable. The operation of this form of the invention is the same as the operation of the invention first described.

In Fig. 3 0f the drawings, still another form of the invention has been shown which resembles that illustrated in Fig. 2. In this form of the invention, similar parts have been referred to by the same reference characters as used in Fig. 2 from which the suffix a hasbeen deleted and the suffix b has been added. In this form of the invention, the core member I2b is identical with that shown in Fig. 2 and is mounted for rotation about the center 20b thereof. Instead of the core member I3a, two other core members 6| and 62 are employed which are similarly discontinuous in form. These core members resemble the core member 1341 and each has poles 63 and 64 and a connecting portion 65 therebetween. On the connecting portions 65 are windings 66 and 61.

The windings 66 and 61 are connected in par allel by means of conductors 1|, 12, 13 and 14, to conductors 15 and 16. The conductor 15 is connected to the variable inductance 35b which, in turn, is connected by a conductor 36b to the variable resistance 31b. This resistance is connected by a conductor 34b to the primary 29b of transformer 21b. The conductor 16 is connected to the other side of the primary 2% of the said transformer.

The principal difference between the form of the invention shown in Fig. 3 and that shown in Figs. 1 and 2 is that the poles lie in proximity to the ends of the distributed winding when the device is at the null point. By means of this construction predetermined non-linear action of the device may be produced. When the distributed winding extends past the poles, so that the span of the winding is greater than that between the poles 63 and 64, no response occurs until after the movable core member has moved throughout a predetermined portion of its course of movement. If the ends of the distributed winding fall short of the poles 63 and 64 so that the span of the distributed winding is less than that between the poles 63 and 64, then the ratio between the induced electromotive force and the extent of movement becomes greatest at initial movement and tapers off as the movement continues. The length of the pole faces along the circumference of the core member carrying the distributed winding determine the rate at which this ratio changes. If the core member II is moved through an angle of 180, another null point will be established and the results produced will be reversed from those just described.

In Figs. 4 and 5, I have shown a form of the invention in which the rotor may turn through-- out an angle greater than 180.

utilized which has a circular portion I62 with a branch I63 extending rearwardly therefrom. The branch I63 is U-shaped in form, having parallel legs I64 and I65 with a connecting portion I66. The leg I64 is in contact with the portion I62, while the leg I65 is situated at the center of said circular portion. Pivoted to the leg I65 by means of a pintle I61 is the movable core member I68 which follows along the circular portion I62. The end of the core member I66 is constructed in the form of a loop and envelops or encircles the circular portion l6 of the core member I6I. For this purpose, two side plates Ill and I12 are employed which are attached to the end of the core member I68 and which have disposed between them outwardly of the portion I62 of core member I6I a spacer member I13. These members form a rectangular opening I14 in the end of the core member I66 which receives the portion I62 and which forms an air gap directing flux from the core member I66 through four sides of the portion I62 of core member I6I.

Wound on the portion I62 of core member I6I is a distributed winding I15 which serves as the output winding of the device and which functions in the same manner as the output winding of the other forms of the invention. The input winding I16 is wound on the connecting portion I66 of the branch I63 and produces the flux in the core member I68 which energizes the wind ing I15.

In Fig. 6, I have shown a form of the invention in which rectilinear instead of rotary movement of the movable member of the invention may be procured. In this form of the invention, a straight elongated core member I8I is employed which has wound on it a distributed winding I62 extending throughout a portion only of the length thereof. The winding I82 constitutes the output winding of this form of the invention. Cooperating with the core member I8I are two U-shaped core members I83 and I84 having legs I85, I66, I81 and I88 with connecting portions I69 and I6I between the respective legs of each core member. These core members are arranged so that the various legs thereof are all in juxtaposed position with reference to the core member I8I, whereby flux may flow from these U- shaped core members and through the portions of the core member I8I lying oppositethe same. The core members I63 and I84 have input windings I92 and I93 thereon which are connected in series by means of a conductor I94. While I have shown these windings on the legs I85 and I68, it can readily be comprehended that these windings may be split and placed partly on the legs I66 and I81, or the same may be placed entirely on the last named legs or mounted on the connecting portions I69 and I9I. The two core members I83 and I64 are fixed relative to one another. These two core members and the winding I82 are mounted for relative movement. This may be accomplished by guiding the winding I82 for movement along the core member I6I, or by In this form-- of the invention, a stationary core member I6I simultaneously guiding the winding I82 and the core member I6I for movement relative to the core members I83 and I64 or, if desired, the core member I8I and the winding I 82 may be held stationary and the core members I66 and I64 simultaneously moved with reference thereto. In all events, the results produced are the same. The method of-use and the results produced by this form of the invention are similar to that descri in the other forms or the invention.

In Fig. 7, I have shown a form or the invention in which the core structure is integral and in which movement is procured by movement of the output winding. In this form of the invention, a core structure 26I is employed which is rectangular in form, having four legs 262, 263, 264 and 265, all connected together to form a closed loop. Issuing outwardly from the leg 264 is another leg 266 which is integral with said leg 264, but is spaced from the leg 262 to form an air gap 261 therebetween. The input winding 268 is mounted on the leg 266, while the output winding 266, which is again a distributed winding, is mounted on the leg 262. In this form of the invention, the winding 266 is made slidable along the core member 262. It will readily be comprehended that two magnetic circuits are produced in the core structure 26I, one including the portion of the core structure to the left of the leg 266 and the other one including the portion to the right of said leg. The number of turns of the winding 266 intercepted by the ilux passing through these magnetic circuits depends upon the position of the said winding with reference to the core member 266. The operation of this form of the invention is similar to that previously described. It will also be comprehended that the leg 262 might be made arcuate and similarly the winding 269. Also, the winding 269 would in such case be supported for rotation about an axis at the center of the arcuate portion of the core structure.

The advantages of my invention are manifest. With my invention, the movement of the movable element can be made to be proportional to the resultant voltage induced in the output winding of the device. Or, if desired, any other performance can be procured. With my invention, changes in the position of the movable member from one side of the null point to the other produces phase shift of exactly whereby certain types of motors particularly adapted for the purpose may be used. Due to the fact that the reluctances of the magnetic paths remain substantially the same throughout movement of the rotatable member, the phase angle between the primary and secondary remains at a constant value as the output is varied through its entire range. By means of the choke and resistance employed, the phase angle between the primary and output can be readily controlled. With my invention, the rotatable member in certain forms of the invention can be rotated substantially through an angle of 180, while in another greater than 270. The movable member of my invention requires a minimum amount of force to operate, since the two magnetic circuits are at all positions of the movable member substantially balanced. Due to the shape and construction of the cores and magnetic elements of the device, the fringe flux is substantially constant, thereby causing the device to operate at all positions in substantially the same manner. With certain of the forms of my invention, sliding contacts can be eliminated.

Changes in the specific form of my invention, as herein described. may be made within the scope of what is claimed without departing from the spirit of my invention.

Having described my invention, what I claim as new and desire to protect by Letters Patent is:

1. An electric control device comprising a core structure including a toroidal shaped core member of magnetic material, a distributed Winding carried only on said core member and extending along a partial extent of the same, a second core member of magnetic material having poles at the extremities thereof disposed adjacent said first core member at different localities, said core structure providing two magnetic circuits, one of said magnetic circuits including the portion of the first core member to one side of one of said poles, the other magnetic circuit including the portion of the first core member on the other side of said pole, said second core member being common to both of said magnetic circuits, a winding on said second core member conductively independent of said distributed winding and adapted on energization to produce fiuxes in said magnetic circuits respectively energizing the portions of said winding on each side of said magnetic pole, and means for guiding said second core member for relative rotational movement with respect to said distributed winding whereby the voltage induced in the distributed winding is proportional to the extent of relative movement.

2. An electric control device comprising a core structure including a toroidal shaped core member of magnetic material, a distributed winding carried only on said core member and extending throughout a portion of the peripheral extent thereof, a second core member of magnetic material having two projecting poles disposed adjacent said first core member on opposite sides thereof, said core structure providing two magnetic circuits, one of said magnetic circuits including the portion of the first core member to one side of one of said poles, the other magnetic circuit including the portion of the first core member on the other side of said pole, said second core member being common to both of said magnetic circuits, a winding on said second core member conductively independent of said distributed winding and energized from a source of power to produce fluxes in said magnetic circuits respectively energizing the portions of said dis tributed winding on each side of said pole dis posed adjacent said distributed winding, and means for guiding said second core member for relative rotational movement about the axis of said first core member.

3. An electric control device comprising a core structure including a toroidal shaped core member of magnetic material, a distributed winding carried onlyon said core member and extending throughout substantially one half the peripheral extent thereof, a second core member- 0f magnetic material having two projecting poles disposed adjacent said first core member and bein situated diametrally opposite one another, said core structure providing two magnetic circuits; one of said magnetic circuits including the portion of the first core member to one side ofsaid poles. the other magnetic circuit including the portion of the first core member on the other side of said poles, said second core member being common to both of said magnetic circuits, a winding on said second core member conductively independent of said distributed winding and energized from a source of power to produce fluxes in said magnetic circuits respectively energizing the portions of said winding on each side of said second core member, and means for guiding said core member for relative rotational movement about the axis of said first core member.

4. In a device of the class described, in combination: a plurality of core means including a plurality of magnetic circuits; one of said core means being continuous having a distributed winding carried on only said one core means spaced thereon over a partial extent of said core means so as to provide a portion thereof covered by said winding and one free from said winding; another of said core means having at least one energizing winding conductively independent of said distributed winding to provide at least one salient pole by which said magnetic circuits are energized; said magnetic circuit traversing portions of said distributed winding; and means for providing relative movement between said distributed winding and said other core means in the direction of the extent of said distributed winding whereby the voltage induced in said dis tributed winding is proportional to the extent of relative movement 5. An electric control device comprising a magnetic core structure including a continuous core member of magnetic material, an elongated distributed winding carried only on said core member and extending along a partial extent of the same,,a discontinuous core member of magnetic material having a pole disposed adjacent said winding and intermediate the ends thereof, said core structure providin two magnetic circuits, one including the portion of said first core member to one side of the pole and the other including the portion of the said first core member to the other side of said pole, said discontinuous core member being common to both of said magnetic circuits, a winding on said second core member conductively independent of said distributed winding and adapted on energization to produce fluxes in said magnetic circuit respectively energizing the portion of said distributed winding on each side of said pole, and means for guiding said distributed winding and said second core member having said pole for relative movement in, the direction of extent of said distributed winding.

6. An electric control device comprising a magnetic core structure including a continuous arcuate core member of magnetic material, a distributed winding carried only on said core member and extending along a partial extent of the same, a second core member of magnetic material having a pole at the extremity thereof disposed adjacent said winding and intermediate to the ends thereof, said core structure providing two magnetic circuits, one including the portion of said first core member to one side of the pole and the other including the portion of said first core member to the other side of said pole, said second core member being common to both of said magnetic circuits, a winding on said second core member conductively independent of said distributed winding and adapted on energization to produce fluxes in said magnetic circuits respectively energizing the portions of said winding on each side of said pole, and pivot means at the axis of said first core member for guiding said core member and said distributed winding for relative rotational movement varying the extent of said distributed winding traversed by the flux flowing in said magnetic circuits whereby the voltage induced in said distributed winding is proportional .to the extent of the relative movement.

7. An electric control device comprising a magnetic core structure including a core member of magnetic material, a distributed winding carried only on said core member and extending along a partial extent of the same, core means of magnetic material having poles at the extremities thereof associated with said core member at localities intermediate the ends of said distributed winding and forming therewith two magnetic circuits, one magnetic circuit including a portion of said core member to one side of said core means and the other magnetic circuit including a portion of said core member to the other side of said core member, electrical conducting means associated with said core means conductively independent of said distributed winding and adapted upon energization to simultaneously produce flux in said magnetic circuit respectively energizing through electromagnetic induction the portions of said winding on each side of said core means, and means for guiding said distributed winding and said core means for relative movement in the direction of extent of said distributed winding and hence varying the extent of said ditributed winding traversed by flux flowing in each magnetic circuit.

8. An electric control device comprising in combination: a magnetic core structure including a continuous core member of magnetic material having two arcuate sections; a distributed winding on only One of said sections and extending along the same; a second core member having projecting poles, one disposed adjacent each of said sections; said core structure providing two magnetic circuits, one including the portions of the sections to one side of said poles and the other including the portions of said sections to the other side of said poles: said second core structure being common to both of said magnetic circuits; a winding on said second core member inductively independent of said distributed winding and adapted on energization to produce fluxes of said magnetic circuits respectively energizing 12 the portions of said winding on each side 01 said poles; and means for guiding said distributed winding and the juxtaposed poles.

9. An electric control device, comprising in combination: a first magnetic core structure including a continuous member of magnetic material having two sections and a distributed winding carried on only one of said sections, extending along the same; a second core structure of magnetic material having at least one projecting pole; said pole bein disposed adjacent to said section carrying said distributed winding; said combined core structures providing two magnetic circuits traversing portions of said distributed winding; a winding on said second core structure conductively independent of said distributed winding and energized from a source of power to produce fluxes in said magnetic circuits; and means for mounting said structures for relative movement between said second core structure and said distributed winding in the direction of extent of said winding, said distributed winding havng an electrical signal induced therein proportional to the extent of said relative movement.

GERARD H. CAINE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 482,421 Cory Sept. 13, 1892 633,690 Franke Sept. 26, 1899 684,579 Miclia'ike Oct. 15, 1901 815,863 Rollinson Mar. 20, 1906 1,566,792 Field Dec. 22, 1925 1,671,963 Alexander June 5, 1928 1,743,794 Murphy Jan, 14, 1930 2,388,977 Johnson Nov. 13, 1945 2,447,212 Schoeppel Aug. 17, 1948 FOREIGN PATENTS Number Country Date 701,823 France Jan. 13, 1931 

